When testing a sensor, it is desirable to gain access at the control module.

When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

Using manufacturer data, identify the control signal circuit for the fuel rail pressure regulator valve.

Ensure the engine is stopped.

Connect PicoScope channel A.

Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.

Select GO or press the space bar to see live data.

Turn on the ignition and wait for the glow plug light to extinguish (if applicable).

Start the engine.

With your live waveform on screen select STOP or press the space bar to stop your capture.

Turn off the engine.

Use the WAVEFORM BUFFER and ZOOM tools to examine your waveform.

Example waveform

Waveform notes

This known good waveform has the following characteristics:

A switched earth, pulse width modulated (PWM), voltage with a fixed cyclic period in which the voltage switches between battery positive at around 15 V and close to battery negative at just above 0 V.

The period the signal spends around 0 V, relative to the total cycle period, indicates the duty of the PWM signal. In this example, approximately one fifth of each cycle is spent close to 0 V, so the PWM duty is about 20%.

The signal cycles five times in a 5 ms period, indicating that it has a base frequency equal to 1000 Hz.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Fuel pressure regulator pressure waveform.

Further guidance

Within a common rail diesel system, the Engine Control Module (ECM) uses a pressure regulator valve to control the fuel pressure within the common rail. When the ECM needs to reduce the pressure, the valve is opened and excess fuel is released to the fuel return system. Conversely, when an increased pressure is needed, the valve is closed.

The pressure regulator valve position is determined by the action of a solenoid against a spring. With these devices, the valve will move from its default position, open or closed depending on the application, when current flows through the solenoid. The greater the current, the greater the displacement of the valve. Thus, in some systems an increase in current will cause the valve to become more open, whereas in others it will cause the valve to become more closed.

The ECM can efficiently control current in a circuit using a PWM signal and, for a given electrical load, the greater the duty period, the greater the average current flowing through the circuit.

With a switched earth activated circuit the solenoid is fed with a constant battery positive on one side and, on the other side the ECM modulates the path to the earth creating current flow. Therefore, the valve is energised ON, when the actuation signal is at battery negative voltage and de-energised OFF, when the actuation signal is at battery positive voltage. Hence the greater the duty cycle, the greater the current in the circuit and the displacement of the valve from its default position.

The ECM will vary the duty depending on the engine speed, load and temperature conditions and the torque demand from the driver, accelerator pedal position.

Disclaimer
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.